High-voltage electric switch having improved supporting base

ABSTRACT

A high-voltage electric switch comprising a plurality of spaced insulator stacks having a switch blade movably supported thereon and a contact jaw supported on one of the other insulator stacks and disposed in the path of movement of the switch blade. The insulator stacks are mounted on a common supporting base which includes a pair of generally parallel channel members and a pair of reinforcing members disposed between said channel members and spaced from the ends of said channel members.

United States Patent [72] Inventor Edmund W. Kuhn Pittsburgh, Pa.

(21] Appl. No. 887,498

[22] Filed Dec. 23, 1969 [45] Patented Oct. 12, 1971 [73] AssigneeWestinghouse Electric Corporation Pittsburgh, Pa.

[54] HIGH-VOLTAGE ELECTRIC SWITCH HAVING IMPROVED SUPPORTING BASE 8Claims, 7 Drawing Figs.

[52] US. Cl 200/48 H0lh 31/00 Field of Search 200/48, 48 RP [5 6]References Cited UNITED STATES PATENTS 3,070,674 12/1962 Gusow 200/48 RP3,284,590 5/1968 Hondalus 200/48 RP 3,316,366 4/1967 Silvy et al. 200/48RP Primary Examiner-Herman J. Hohauser Att0meysA. T. Stratton and C. L.McI-Iale PATENTEDUCT 12 I971 SHEET 10F 2 HIGH-VOLTAGE ELECTRIC SWITCHHAVING IMPROVED SUPPORTING BASE BACKGROUND OF THE INVENTION Thisinvention relates to high-voltage electric switches and, moreparticularly, to supporting base structures which form part of suchswitches.

In the construction of certain types of high-voltage switches such aspolyphase or three-phase disconnecting switches, a plurality of poleunits or switch units is mounted or supported on a common supportingstructure in side-by-side relation. Each pole unit of such a switchnormally includes a supporting base on which a plurality of spacedinsulator stacks is mounted or secured with a switch arm or contact armmovably supported on one or more of the insulator stacks and a contactjaw supported on one of the other insulator stacks.

It has been found that in the operation of such a polyphase switch, whena short circuit or abnormal operating condition occurs in the electricalsystem in which the switch is connected, the supporting base of eachpole unit of the switch is subjected to torsional or twisting stressesor forces due to the interacting effects between adjacent pole units.

In order to support each pole unit of such a polyphase switch bothduring normal and abnormal operating conditions such as that justindicated, various types of supporting base constructions have beenproposed for such switches. One type of base structure which has beenproposed for this type of switch includes a plurality of extrudedaluminum structural members, such as described in U.S. Pat. No.3,284,590. An important disadvantage of such a base structure is that ithas been found to be prohibitive in cost. Another type of base structurewhich has been employed in polyphase switches of the type describedincludes a plurality of structural steel members and plates which arewelded or bolted together, such as shown in U.S. Pat. No. 3,316,366which issued Apr. 25, 1967 and is assigned to the same assignee as thepresent application. A base structure of the latter type has been foundto have certain disadvantages in that it is relatively complicated inconstruction and requires a number of metal joining and formingoperations to form a base structure having adequate resistance to thetorsional stresses of the type described which may result during theoperation of a polyphase or three-phase switch.

SUMMARY OF THE INVENTION In accordance with the invention, ahigh-voltage electric switch includes a switch blade or contact armhaving one end movable into and out of engagement with an associatedcontact jaw. The switch blade and the contact jaw are supported on aplurality of spaced insulator stacks which are supported on and securedto a common supporting base. The base comprises a pair of elongated,metallic channel members, each of which includes a pair of spacedintegral sidewall or flange portions connected by a bight portion. Thechannel members are disposed generally parallel to and spaced from oneanother with the corresponding sidewall or flange portions of therespective channel members projecting away from those of the otherchannel member in opposite directions. The base also includes a pair ofreinforcing members disposed adjacent to and spaced from each of theopposite ends of the base. Each reinforcing member includes an elongatedtubular member which is disposed between and generally parallel to theassociated channel members. The tubular member is preferably circular incross section and is formed from a metallic material which is preferablysteel.

Each reinforcing member also includes a pair of generally rectangularmetallic plates which are disposed between and generally transverselywith respect to the associated channel members and which are secured tothe opposite ends of the associated tubular member. The pair of platesof each reinforcing member are also secured at the opposite sidesthereof by suitable means, such as welding, to the respective channelmembers, more specifically to the bight portions of said channelmembers. In addition to the above pair of reinforcing members, the basealso includes a pair of generally rectangular, metallic reinforcingplates which are disposed between the associated channel memberssubstantially at the opposite ends thereof generally transversely withrespect to said channel members. The latter reinforcing plates aresecured at the opposite sides thereof to the associated channel membersby suitable means, such as welding.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects of the invention will beapparent from the following detailed description taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a partial view, in side elevation, of a high voltage electricswitch structure embodying the principal features of the invention;

FIG. 2 is a top plan view of a portion of the supporting base whichforms part of the switch structure shown in FIG. I;

FIG. 3 is a side elevational view of the supporting base shown in FIG.2;

FIG. 4 is a bottom view of the supporting base shown in FIGS. 2 and 3;

FIG. 5 is an enlarged end elevational view taken along the line V--V inFIG. 3, of the supporting base shown in FIGS. 2, 3 and 4;

FIG. 6 is an enlarged view in side elevation of a reinforcing memberwhich forms part of the supporting base shown in FIGS. 2 through 5; and

FIG. 7 is an enlarged view in end elevation of the reinforcing membershown in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawingsand FIG. I in particular, there is shown a high-voltage disconnectingswitch assembly 10 which normally forms one pole unit of a polyphase orthree-phase high-voltage switch structure which includes a plurality ofdisconnecting switch assemblies each having the construction of thedisconnecting switch assembly I0 and supported on a common supportingstructure which may include a plurality of structurally supporting crossmembers, as indicated diagrammatically at 202 at 204 in FIG. I. In sucha polyphase switch structure, a plurality of pole units, such as thedisconnecting switch assembly 10, is mounted in side-byside spacedrelation upon the common supporting structure.

The disconnecting switch assembly 10 comprises three spaced insulatorstacks 32, 34 and 36 which are mounted upon a common supporting base 30which will be described in detail hereinafter. The operating parts ofthe disconnecting switch assembly 10 which are mounted at the upper endsof the insulator stacks 32, 34 and 36, as viewed in FIG. I, aredescribed in detail in U.S. Pat. No. 3,194,905 which issued July 13,I965 to F. W. Jewell et al. and which is assigned to the same assigneeas the present application. Each of the insulator stacks 32, 34 and 36comprises a plurality of insulators which are preferably formed fromporcelain or other suitable electrically insulating material. The numberof insulators required in each of the insulator stacks 32, 34 and 36depends upon the voltage of the electrical system in which thedisconnecting switch 10 is applied. As illustrated, the insulator stacks32 and 34 may be mounted upon the fixed pedestals or spacers I32 and134, respectively, which, in turn, may be secured to the top of theassociated supporting base 30. As described in the last mentionedpatent, the insulator stack 36 is mounted upon a shaft 165, he lower endof which is rotatably mounted in a bearing member 163 which is securedto the top of the associated supporting base 30. As shown in FIG. I, anoperating lever or crank arm 162 may be secured to the shaft I65 at thelower end of the insulator staff 36 to rotate the insulator stack 36with the crank arm 162 being adapted for connection or coupling to anyconventional means for operating the crank arm 162 to effect rotation ofthe associated shaft 165 and the insulator stack 36 about its ownlongitudinal axis. A shaft 169 is secured to and extends upwardly fromthe upper end of the insulator stack 36 to thus form an operativeextension of the shaft 165 which is provided at the lower end of theinsulator stack 36 in order to positively connect the crank arm 162 andthe insulator stack 36 to the balance of the operating mechanism of thedisconnecting switch assembly which will be described hereinafter. Theshaft 169 passes through an opening provided in the terminal end castingor member 120 which is substantially aligned with the axis of rotationof the shaft 169 and the insulator stack 36 and has mounted at the upperend thereof a crank arm 110 which is rotatable with the shaft 169 andwhich extends generally at an angle or generally transversely withrespect to the axis of rotation of the shaft 169.

As illustrated in FIG. I, the disconnecting switch 10 includes agenerally U-shaped relatively stationary contact assembly or break jawassembly 40 which is mounted on and secured to the top of the insulatorstack 32. The stationary contact assembly 40 includes a plurality ofpairs of spaced contact jaws 43 which are mounted on and interconnectedby an associated base member 41 which is forged or cast from anelectrically conducting material, such as copper, and which is securedto the top of the insulator stack 32 by suitable means such as aplurality of bolts (not shown). A terminal pad 142 which is adapted toreceive a terminal connector may be formed integrally with or secured toone side of the base member or terminal casting 41. Where desired, arelatively stationary arcing horn 45 may also be secured to the terminalcasting 41.

In order to provide an electrically conducting path between thestationary contact assembly 40 and the electrically conducting parts ofthe disconnecting switch 10 which are mounted on top of the insulatorstack 34 when the switch 10 is in a closed circuit operating condition,as shown in FIG. 1, a movable switch blade or contact arm 50 isprovided. The blade 50 is elongated in shape and includes a main body orcentral portion which may be generally tubular in configuration andwhich is formed from an electrically conducting material, such as copperor aluminum. The blade 50 also includes an end portion at its left endwhich may be generally rectangular in cross section to providehigh-pressure contact areas which are adapted to engage the contact jaws43 of the stationary contact assembly 40. Where desired, a relativelymovable arcing horn 51 may be mounted at the free or left end of theblade 50 which is adapted to cooperate with the relatively stationaryarcing horn 45 previously mentioned.

In order to support the blade 50 for rotation about its own axis and forarcuate movement about an axis which extends generally perpendicular tothe axis of the blade 50, as viewed in FIG. 1, the right end of theblade 50 may be secured to a generally tubular crank member 60 formovement therewith, as described in detail in the Jewell et al. patentpreviously mentioned. In order to support the crank member 60, as wellas the blade 50, for rotation about a common axis which extendslongitudinally of the blade 50, a hinge member 70 having a generallytubular portion is provided and the crank member 60 is rotatablysupported on said hinge member, as described in the Jewell et al. patentpreviously mentioned. An electrically conducting path may be providedbetween the crank member 60 and the hinge member 70 by one or moreresilient electrically conducting members (not shown) disposed betweenthe crank member 60 and the tubular portion of the hinge member 70. I

In order to support the hinge member 70 for rotation about an axis whichis generally perpendicular to the axis of the blade 50 and to supportthe blade 50 which is assembled with the hinge member 70 as justindicated for arcuate movement or travel about said axis, the spacedarms 82 (only one shown) of the hinge support member or frame 80 aredisposed on opposite sides of the hinge member 70. The hinge member 70includes a pair of hinge portions which project generallyperpendicularlywith respect to the axis of the tubular portion of the 1hinge member 70 with the hinge member 70 being pivotally supportedbetween the arms 82 of the hinge support frame 80 by electricallyconducting hinge pins or studs 81 as described in the Jewell et al.patent. The electrically conducting hinge pins 81 which support thehinge member 70 may be electrically connected to the hinge member 70 byone or more resilient electrically conducting members (not shown) whichmay be disposed inside the generally tubular hinge portions of the hingemember 70 to engage both the hinge member 70 and the hinge pins 81 whichare secured to the arms 82 of the hinge support frame 80. In order toprovide an electrically conducting path between the hinge support memberand the terminal casting 120, an electrically conducting tubular member152 may be provided which structurally and electrically connects thehinge support member 80 and the terminal end member 120. Theelectrically conducting member 152 may also serve as a housing for acounterbalancing mechanism which is described in detail in U.S. Pat. No.3,074,474 which issued Feb. 26, 1963 to E. F. Beach et al. and which isassigned to the same assignee as the present application.

In order to operatively connect the crank arm 110 which is mounted onthe shaft 169 which is secured to the top of the rotatable insulatorstack 36 and the crank member 60 and to actuate the movement of theblade 50 during opening and closing operations of the disconnectingswitch 10, the disconnecting switch 10 includes the operating link whichis pivotally connected to the crank member 60, the slip joint 92 and theuniversal joint which operatively connects the slip joint 92 to thecrank arm 110. The slip joint 92 and the universal joint 100 aredescribed in detail in the Jewell et al. patent previously mentioned.

In general, the supporting base 30 of the disconnecting switch 10 isprovided to support the weights of the insulator stacks 32, 34 and 36,as well as the weights of the parts of the disconnecting switch 10 whichare mounted at the top of the respective insulator stacks, and also toresist the torsional or twisting stresses which result in the supportingbase 30 where the disconnecting switch 10 forms one pole unit of apolyphase or three-phase switch structure due to the interaction of therespective pole units of such a polyphase switch structure during shortcircuit or other abnormal operating conditions. As previously indicated,the insulator stacks 32, 34 and 36 are supported on the supporting base30 in spaced relation and are disposed generally perpendicular to theoverall supporting base 30 as shown in FIG. 1.

More specifically, the supporting base 30 comprises a pair of elongatedchannel members 33 and 35 which are disposed generally parallel to andspaced from one another, as best shown in FIGS. 2 through 5. The channelmembers 33 and 35 are preferably formed from a metallic material, whichis preferably steel. Each of the channel members 33 and 35 includes apair of spaced integral sidewall or flange portions, as indicated at 33Aand 33C for the channel member 33 and as indicated at 35A and 35C forthe flange member 35, which are interconnected by an associated bightportion as indicated at 338 and 358 for the channel members 33 and 35,respectively. As shown in FIG. 5, the channel members 33 and 35 whichmake up the supporting base 30 are assembled with the correspondingpairs of side wall portions 33A and 33C and 35A and 35C, respectively,projecting outwardly or away from one another in opposite directions.The bight portions 33B and 35B of the channel members 33 and 35,respectively, are disposed in back to back relation and spaced from oneanother as shown in FIG. 5.

In order to provide the supporting base 30 with adequate structuralstrength to resist the torsional stresses which may result during theoperation of the disconnecting switch 10, as previously mentioned, apair of reinforcing members 20 is disposed adjacent to the opposite endsof the supporting base 30 and spaced from said opposite ends, as bestshown in FIGS. 2 through 4. Each of the reinforcing members 20 includesan elongated tubular member 22 which is disposed between and generallyparallel to the associated channel members 33 and 35. Each of thereinforcing members 20 also includes a pair of generally rectangularplates 24 which are disposed between and generally transversely orperpendicularly with respect to the channel members 33 and 35, as shownin FIGS. 2 through 4. Both the tubular member 22 and the associatedgenerally rectangular plates 24 of each of the reinforcing members 20are formed from a metallic material which is preferably steel. Thetubular member 22 of each of the reinforcing members 20 is preferablycircular in cross section and the associated generally rectangularplates 24 are secured to the opposite ends of the associated tubularmember 22 by suitable means, such as welding, as shown in FIGS. 6 and 7.The generally rectangular plates 24 of each of the reinforcing members20 are, in turn, secured at the opposite sides thereof to the bightportions of the associated channel members 33 and 35 by suitable means,such as welding, as best shown in FIG. 5. It is to be noted that each ofthe generally rectangular plates 24 which form part of the reinforcingmembers 20 includes a pair of recesses 24A and 248 at the opposite sidesthereof to limit the portions of the plates 24 which must be welded tothe associated channel members 33 and 35 at the sides of each of saidplates. If the recesses 24A and 24B were not provided in each of thegenerally rectangular plates 24, the entire sides of each of said plateswould have to be welded to the associated channel members 33 and 35respectively in order to avoid the entrapment of certain solutions orliquids which are normally employed in the galvanizing of the entiresupporting base 30 after the reinforcing members 20 are assembled withand secured to the associated channel members 33 and 35 as shown inFIGS. 2 through 4.

In addition to the reinforcing members 20, a pair of generallyrectangular reinforcing plates 26 is disposed substantially at theopposite ends of the supporting base 30 with said plates being disposedbetween and generally transversely or perpendicularly with respect tosaid channel members, as shown in FIGS. 2 through 5. Each of thereinforcing plates 26 is secured at the opposite sides thereof to therespective channel members 33 and 35 by suitable means, such as welding,with the reinforcing plates 26 being formed from a metallic materialwhich is preferably steel. Each of the reinforcing plates 26 includes apair of recesses 26B and 26C at the opposite sides thereof for the samereasons previously described in connection with the plates 24. Each ofthe reinforcing plates 26 also includes a central opening, as indicatedat 26A, to permit the mounting of strain insulators (not shown), wheredesired, to permit the supporting of associated electrical conductorswhich may be associated with or connected to the disconnecting switch10. It is important to note that the reinforcing plates 26 providedsubstantially at the opposite ends of the supporting base 30structurally complete a boxlike structure which is formed by the overallsupporting base 30 and also assist in providing the supporting base 30with resistance to the torsional or twisting stresses previouslymentioned. Where desired, additional reinforcing plates such as thereinforcing plate 27 may be disposed between and secured to the channelmembers 33 and 35 at axially spaced locations along the overall lengthof the supporting base 30 to provide additional rigidity in certainapplications.

Referring again to FIG. 1, it is important to note that the constructionof the supporting base 30 permits the mounting of the pole units of apolyphase switch structure, such as the disconnecting switch unit 10, tobe mounted on common structural cross members such as those indicateddiagrammatically at 202 and 204 in FIG. 1 with the opposite ends of thesupporting base 30 of each pole unit of disconnecting switch overhangingthe associated structural cross support members by a predetermineddistance, as indicated at 210 in FIG. 1.

For example, in one typical application of the disclosed construction ofthe supporting base 30, each of the reinforcing members wasapproximately 16 inches long and were each spaced from the adjacent endof the supporting base 30 by approximately 11 inches to permit a maximumoverhanging distance of each of the opposite ends of the supporting baseof approximately 30 inches where desired. The positioning of thereinforcing members 20 adjacent the opposite ends of the supporting base30 transmits the torsional stresses or forces which may result duringshort circuit conditions to the reinforcing members 20 and then to thecommon supporting structure as indicated diagrammatically at 202 and 204in FIG. I and limits the deflection of the supporting base 30 atdifferent points during such operating conditions to predeterminedminimum values which avoid any consequent damage to the disconnectingswitch 10 during such operating conditions. The improved torsionalrigidity of the supporting base 30 has been found also to result inequal structural restraint of all of the insulator stacks 32, 34 and 36regardless of the relative position of the supporting cross members 202and 204 within a limited range of locations which extends from right atthe opposite ends of the supporting base 30 to locations which result ina predetermined overhang distance at each end of said base as previouslyindicated.

In the overall operation of the disconnecting switch 10, as described ingreater detail in the Jewell patent previously mentioned, when the shaft165 is rotated by an external means through the crank am 162, the blade50 is first rotated about its own axis to effect a disengagement of thefree end of the blade 50 from the contact jaws 43 of the stationarycontact assembly 40. Continued movement of the crank arm 110 in thepredetermined direction actuates an arcuate movement of the blade 50along with the hinge member 70 in a clockwise direction aboutthe axisdefined by the hinge pins which support the hinge member 70 until theblade 50 is in a substantially vertical position as viewed in FIG. 1which is angularly displaced from the position of the blade shown inFIG. I by substantially During a closing operation of the disconnectingswitch 10, the crank arm 162 is actuated in the opposite direction tothereby actuate the crank arm in such a direction as to first actuatethe blade 50 from the substantially vertical position just indicated toa position which is substantially parallel to the supporting base 30 asshown in FIG. 1. Further rotation of the crank arm 110 then rotates theblade 50 about its own axis to establish contact pressure between thefree end of the blade 50 and the stationary contact assembly 40. Insummary, the operating mechanism of the disconnecting switch 10separates the rotary movement of the blade 50 about its own axis whichis necessary to either disengage the left end of the blade 50 from thestationary contact assembly or to actuate said blade to fully engage thestationary contact assembly 40 and the generally arcuate movement ofsaid blade between the open and closed positions just described.

It is to be understood that the teachings of the invention may beapplied to other types of high-voltage electric switches whose operatingparts may differ from those of the disconnecting switch 10 asillustrated.

The apparatus embodying the teachings of this invention has severaladvantages. For example, a high-voltage switch construction as disclosedincludes an improved supporting base which is uniquely adapted to permitthe use of steel structural members in a relatively simple constructionwhile providing the resistance to torsional stresses or forces which arerequired in a polyphase switch structure due to the interaction ofadjacent pole units during certain operating conditions. In addition,the disclosed supporting base construction permits the associatedsupporting cross members for the adjacent pole units of polyphase switchstructure to be mounted either adjacent to the opposite ends of therespective supporting bases of the different pole units or to locate thesupporting cross members 202 and 204 inwardly from the opposite ends ofthe supporting base by a predetermined distance, as indicated by theaxially spaced mounting holes 38 which are provided on the lower flangeor sidewall portions 33C and 35C of the channel members 33 and 35,respectively as best shown in FIG. 4. More specifically, the disclosedsupporting base construction lends itself to convenient assembly withthe supporting cross members indicated diagrammatically at 202 and 204in FIG. 1 by suitable fastening means such as a plurality of spacedbolts which may pass through the openings 38 provided in the bottomsidewall portions of the channel members 33 and 35 as shown in FIG. 4.

The insulator stacks 32, 34 and 36 may be conveniently secured to theassociated channel members and more specifically to the upper sidewallportions 33A and 35A of said channel members by suitable fasteningmeans, such as a plurality of axially spaced bolts which pass throughthe axially spaced openings 39. it important to note that the disclosedsupporting base 30 also provides the necessary rigidity and structuralstrength to support the weight of each of the insulator stacks 32, 34and 36 as well as the switch operating parts which are disposed on topof the respective insulator stacks. In summary, the applicant'sconstruction permits the use of steel structural members to fonn animproved supporting base for high-voltage electric switches in arelatively less complicated overall structure while providing. thenecessary resistance to torsional or twisting stresses which may resultdue to short circuit conditions in the operation of a polyphase orthree-phase switch structure having a plurality of pole units disposedin side-byside relation.

I claim as my invention:

1. A high-voltage electric switch comprising a base, a plurality ofspaced insulator stacks mounted on said base, a switch blade movablysupported on top of at least one of said insulator stacks a contact jawsupported on top of another of said insulator stacks to be engaged bysaid blade in one operating position of said blade, said base comprisinga pair of elongated, metallic channel members each having a pair ofspaced sidewall portions, said channel members being disposed generallyparallel and spaced from one another with the sidewall portions of eachof said channel members projecting away from those of the other channelmember in opposite directions, and a pair of reinforcing membersdisposed adjacent to and spaced from each of the opposite ends of saidbase, each reinforcing member including a metallic, elongated tubularmember disposed between and generally parallel to said channel membersand a pair of generally rectangular, metallic plates disposed betweenand generally transversely with respect to said channel members, saidpair of generally rectangular, metallic plates being secured to theopposite ends of said tubular member and secured at the opposite sidesthereof to the respective channel members.

2. The combination as claimed in claim 1 wherein the tubular member ofsaid reinforcing is generally circular in cross section.

3. The combination as claimed in claim 1 wherein an additional pair ofgenerally rectangular, metallic plates are disposed substantially at theopposite ends of said base between and generally transversely withrespect to said channel members, said last-mentioned plates beingsecured at the opposite sides thereof to the respective channel members.

4. The combination as claimed in claim I wherein said channel membersand said reinforcing members are formed primarily from steel.

5. The combination as claimed in claim 1 wherein each of the sidewallportions of said channel members at the top of said base includes aplurality of spaced openings and a plurality of fastening means isprovided to secure said insulator stacks to said base, said fasteningmeans being disposed to pass through the openings in the sidewallportions of said channel members.

6. The combination as claimed in claim 1 wherein the pair of generallyrectangular plates of each of said reinforcing members are welded to theopposite ends of the tubular member of said reinforcing member and thesides of said plates are welded to the respective channel members.

7. The combination as claimed in claim 2 wherein an additionalpair ofgenerally rectangular, metallic plates is disposed substantially at theopposite ends of said base between and generally transverse with respectto said channel members, said additional pair of plates being secured atthe opposite sides thereof to the respective channel members.

8. The combination as claimed in claim 2 wherein the pair of generallyrectangular plates of each reinforcing member are welded to the oppositeends of the tubular member of said reinforcing member and the sides ofsaid plates of each member are welded to the respective channel members.

1. A high-voltage electric switch comprising a base, a plurality ofspaced insulator stacks mounted on said base, a switch blade movablysupported on top of at least one of said insulator stacks a contact jawsupported on top of another of said insulator stacks to be engaged bysaid blade in one operating position of said blade, said base comprisinga pair of elongated, metallic channel members each having a pair ofspaced sidewall portions, said channel members being disposed generallyparallel and spaced from one another with the sidewall portions of eachof said channel members projectinG away from those of the other channelmember in opposite directions, and a pair of reinforcing membersdisposed adjacent to and spaced from each of the opposite ends of saidbase, each reinforcing member including a metallic, elongated tubularmember disposed between and generally parallel to said channel membersand a pair of generally rectangular, metallic plates disposed betweenand generally transversely with respect to said channel members, saidpair of generally rectangular, metallic plates being secured to theopposite ends of said tubular member and secured at the opposite sidesthereof to the respective channel members.
 2. The combination as claimedin claim 1 wherein the tubular member of said reinforcing is generallycircular in cross section.
 3. The combination as claimed in claim 1wherein an additional pair of generally rectangular, metallic plates aredisposed substantially at the opposite ends of said base between andgenerally transversely with respect to said channel members, saidlast-mentioned plates being secured at the opposite sides thereof to therespective channel members.
 4. The combination as claimed in claim 1wherein said channel members and said reinforcing members are formedprimarily from steel.
 5. The combination as claimed in claim 1 whereineach of the sidewall portions of said channel members at the top of saidbase includes a plurality of spaced openings and a plurality offastening means is provided to secure said insulator stacks to saidbase, said fastening means being disposed to pass through the openingsin the sidewall portions of said channel members.
 6. The combination asclaimed in claim 1 wherein the pair of generally rectangular plates ofeach of said reinforcing members are welded to the opposite ends of thetubular member of said reinforcing member and the sides of said platesare welded to the respective channel members.
 7. The combination asclaimed in claim 2 wherein an additional pair of generally rectangular,metallic plates is disposed substantially at the opposite ends of saidbase between and generally transverse with respect to said channelmembers, said additional pair of plates being secured at the oppositesides thereof to the respective channel members.
 8. The combination asclaimed in claim 2 wherein the pair of generally rectangular plates ofeach reinforcing member are welded to the opposite ends of the tubularmember of said reinforcing member and the sides of said plates of eachmember are welded to the respective channel members.